In last months tube presentation of the 6BL7 I briefly mentioned this tube. Have a look at the 6BX7.
The 6BX7 belongs to a family of 3 medium mu double triodes along with the 6SN7 and 6BL7. They differ in amplification factor, transconductance and plate resistance.
All 3 of them share the same octal base. The 6BX7 has the lowest amplification factor of them with a mu of 10. But this comes with a low plate resistance of 1300 Ohm. Wire both triodes in the bottle in parallel and this halves to 650 which is in the territory of a 2A3 output tube. This is one hefty triode for such a small bottle. Its characteristics would also make this an excellent driver tube with quite large voltage swing capability. Besides a flea power tube amp it would also serve well in a headphone application or line preamplifier. Another tube which is rather forgotten but deserves more attention. I did not have any of these in stock, but after covering the 6BL7 last month I thought it would be a good idea to get some for completing the series of 3 cousin medium mu double triodes. To my surprise they were easy to find at modest prices. As always we will start with a look at the plate curves both from the datasheet and from a real life sample.
I only got some 6BX7GT from 2 different manufacturers. Here some made by General Electric:
From RCA I have samples with three different construction styles.
The first one has a clear top and the getter on the side.
Those little boxes on the top are cooling fins for the grids.
Next we have a coin base version:
And lastly a version with the getter applied in the top dome.
And now the tube in operation:
What a neat device. So many tubes, so little time to try them all.
Best regards
Thomas
